linux-kernel - Re: [PATCH 2.4.32] Fix AVM C4 ISDN card init problems with newer CPUs

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Message-Id: <1154685646.23655.185.camel@localhost.localdomain>
Date:	Fri, 04 Aug 2006 11:00:46 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Karsten Keil <kkeil@...e.de>
Cc:	Jukka Partanen <jspartanen@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.4.32] Fix AVM C4 ISDN card init problems with newer
	CPUs

Ar Iau, 2006-08-03 am 19:31 +0200, ysgrifennodd Karsten Keil:
> Yes, that should be go in.
> 
> AVM C4 ISDN NIC: Add three memory barriers, taken from 2.6.7,
> (they are there in 2.6.17.7 too), to fix module initialization
> problems appearing with at least some newer Celerons and
> Pentium III.
> 
> Acked-by: Karsten Keil <kkeil@...e.de>
> Signed-off-by: Jukka Partanen <jspartanen@...il.com>

NAK: Alan Cox <alan@...hat.com>

Two reasons

#1	You should use cpu_relax in such loops
#2	The readl (which c4inmeml is a pointless #define of) is defined to be
a volatile reference itself

That means that the real bug would appear to be different and either you
have a gcc bug which is possible or you have something stranger going
on, such as the continued polling busying the microcontroller the other
end, in which case you need a delay not the lucky chance that mb() is
slowish on some x86 systems.

So you either want

		cpu_relax + other fixes
	or	udelay(something)


Alan

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